The present invention relates to a heat radiating insulator for a coil. The insulator is used, for example, after hardening to securely hold, for example, a stator coil and/or a rotor coil of an electric motor of an automobile electric component, and to effectively prevent overheating of the stator coil and/or the rotor coil.
In rotary equipment such as an electric motor of an automobile electric component, the stator section has a configuration as shown in FIGS. 1 and 2. Referring to FIGS. 1 and 2, a core 11 comprises a laminate body of a number of silicon steel sheets and has a cylindrical opening for receiving a rotor (not shown). A number of slots 12 are formed in the inner surface of the cylindrical opening of the core 11. An insulator layer 13 is formed on the outer end surface of the core 11, and on the inner cylindrical surface having these slots 12. A stator coil 14 is mounted to the core 11 having the insulator layer 13 by being fitted within the slots 12. An insulator 15 is coated over the stator coil 14 to fix the stator coil 14.
In equipment with a stator coil of the configuration described above, heat is generated upon flowing a current through the stator coil 14, as shown in FIG. 3. Heat is then conducted to the core 11 through the insulator layer 13, or is radiated into the air through the insulator 15 fixing the stator coil 14. The insulator layer 13, also formed on the slots 12, generally comprises an epoxy powder, polyester, paper, a resin, or the like. The insulator 15 for fixing the stator coil 14 generally comprises an epoxy powder, epoxy coating, polyester coating, polyimide coating or the like. The parts of the stator coil of the configuration as described above have the thermal conductivities shown in Table 1 below:
TABLE 1 ______________________________________ Thermal Conductivity Parts Material (cal/cm .multidot. deg .multidot. sec) ______________________________________ Core Iron 1.5 .times. 10.sup.-1 Coil Copper 9.2 .times. 10.sup.-1 Insulator Plastics 3-5 .times. 10.sup.-4 ______________________________________
As can be seen from Table 1, the thermal conductivity of the insulator is extremely low compared to that of other parts of the coil. This means that the insulator is the single most significant factor responsible for the temperature rise in the coil. In an electric motor or the like, during overheating, the output decreases due to copper loss resulting from the temperature rise. Thus, the magnet wire for the coil must be heat resistant, and the manufacturing cost is high.
In order to solve these problems, it has been proposed to improve heat radiation by mixing in fine particles of an inorganic material, for example, alumina powder or calcium carbonate, into a synthetic resin composition. However, when a relatively large amount of fine particles is added so as to improve heat radiation, mechanical strength is lowered and electrical insulation performance is degraded. For example, when calcium carbonate is used, the heat radiation effect obtainable is either limited or otherwise unsatisfactory.